1. Field of the Invention
The present invention relates to a wrench with a fixed maximum operational torque to prevent damage to the object secured by a fastener driven by the wrench. The present invention also relates to a wrench with a fixed maximum operational torque, wherein damage to the object secured by a fastener driven by the wrench is avoided when the wrench is turned in a direction, and wherein the fastener is forced to turn when the wrench is turned in a reverse direction.
2. Description of the Related Art
FIG. 16A of the drawings illustrates a conventional wrench 1 having a hexagonal driving portion with six planar faces 2 for engaging with six faces of a hexagonal groove in a top face of a fastener. However, slide tends to occur between the planar faces of the driving portion of the wrench 1 and the faces of the fastener. FIG. 16B illustrates a so-called TROX wrench 3 having plural arcuate faces 4 for engaging with corresponding arcuate faces in a top face of a fastener. Such a TROX wrench 3 is used to tighten important parts of a car and cutting tools. As illustrated in FIG. 17, a blade 7 is tightened to a cutting tool 5 by a bolt 6. However, the expensive blade 7 tends to be damaged when the bolt 6 is excessively tightened. But the blade 7 could fly away and thus cause injury if the bolt 6 is not tightened to the desired extent.
An object of the present invention is to provide a wrench with a fixed maximum operational torque such that when the torque applied by the user is greater than the maximum operational torque, the wrench slides and the fastener is not turned. Thus, damage to the object secured by the fastener is prevented.
Another object of the present invention is to provide a wrench with a fixed maximum operational torque that can be altered in response to the actual use.
A further object of the present invention is to provide a wrench with a fixed maximum operational torque, wherein damage to the object secured by a fastener driven by the wrench is avoided when the wrench is turned in a direction, and wherein the fastener is forced to turn when the wrench is turned in a reverse direction.
In accordance with a first aspect of the invention, a wrench comprises:
a rod comprising a driving portion on an end thereof for engaging with a fastener;
a retainer having a central portion securely mounted to the rod to turn therewith, the retainer including at least two pairs of retaining sections on a side thereof;
a casing comprising a receiving section for accommodating the retainer and allowing relative rotational movement between the casing and the retainer, the casing further comprising a compartment communicated with the receiving section;
a pressing member received in the compartment of the casing and slidable along a longitudinal direction of the rod, the pressing member being turned together with the casing when the casing is turned; and
means for biasing two ends of the pressing member to respectively engage with one pair of the retaining sections of the retainer, thereby exerting an engaging force between each of the ends of the pressing member and an associated one of the retaining sections of the retainer;
wherein when a rotational force applied to the casing is smaller than the engaging force, the retainer and the rod are turned to thereby turn the fastener; and
wherein when the rotational force applied to the casing is greater than the engaging force, the casing and the pressing member slide while the retainer and the rod are not turned.
In accordance with a second aspect of the invention, a wrench comprises:
a rod comprising a driving portion on an end thereof for engaging with a fastener;
a retainer having a central portion securely mounted to the rod to turn therewith, the retainer including a plurality of annularly spaced retaining sections on a side thereof;
a casing comprising a receiving section for accommodating the retainer and allowing relative rotational movement between the casing and the retainer, the casing further including a compartment communicated with the receiving section;
a pressing member received in the compartment of the casing and slidable along a longitudinal direction of the rod, the pressing member being turned together with the casing when the casing is turned, the pressing member including at least one engaging member; and
means for biasing said at least one engaging member of the pressing member to selectively engage with at least one of the retaining sections of the retainer, thereby exerting an engaging force between said at least one engaging member of the pressing member and said at least one of the retaining sections of the retainer;
wherein when a rotational force applied to the casing is smaller than the engaging force, the retainer and the rod are turned to thereby turn the fastener; and
wherein when the rotational force applied to the casing is greater than the engaging force, the casing slides and said at least one engaging member slides to another one of the retaining sections of the retainer while the retainer and the rod are not turned. (FIGS. 2, 9, 11, 15)
Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.